Suppressing Non-Delivery Reports (NDRs)

Once the spammers find your domain, which usually only takes a few weeks after it has come online, you'll start seeing lots of error messages being returned to your Exchange Server - for email that was never sent from your server! This is commonly called back scatter, and can be worse than spam itself. Viruses, worms, adware and other types of malicious software can all cause your Exchange Server to generate NDRs - Non-Delivery Reports. NDRs traditionally meant that a mailbox was full or that a particular user is no longer at a particular company.

Unfortunately, with the explosion of spam and malware over the last few years, their usefulness is at an all-time minimum. Today, many Exchange Administrators choose to turn them off. This is done in the window displayed below (on Exchange Server 2003 - a similar setting exists in Exchange Server 2007).

You access this window by opening ESM. Expand Global Settings, click on Internet Message Formats in the left pane, then right-click on the Default label in the right pane. Finally, select Properties, and then click on the tab named Advanced. The six check-boxes at the bottom of this page control a number of interesting behaviors. It is worthwhile to click on the Help button, and explore what each of them does. For right now you are only interested in the fifth box and except for this particular box, "Allow non-delivery reports", the default settings for these items are normally just fine.

In order to disable the generation of non-delivery reports, simply uncheck the box, and click OK. The effect is immediate and no new NDRs will be generated. However, if there are NDRs already in your SMTP outgoing queues (very likely), they will take a couple of days for them to filter out.

Until next time...

As always, I hope you've enjoyed this article. If there are topics you are interested in and would like for me to cover, please send me an e-mail or post in the local forums.